Such a device serves fundamentally for the correction of parameters in the raster deflection, for example the correction of north/south and east/west distortions, of pin-cushion distortions, of nonlinearities in the deflection, and other geometric distortions in the horizontal or vertical directions. A particular field of application is convergence correction in a television projection receiver in which the pictures of three monochromatic picture tubes are projected onto a picture surface. The television receiver is understood as any receiver in which pictures are reproduced electronically or using a raster. The receiver can be fed from an arbitrary video signal source with a conventional television broadcast signal, or as a pure monitor with an RGB signal, an FBAS signal or, separately, with a luminance signal and a colour carrier.
The correction of the deflection parameters is undertaken with the aid of correction values which are stored in a convergence circuit. The correction values have been determined from a multiplicity of individual receivers from a specific series in such a way that the best correction is achieved on average. The correction values stored in the convergence circuit are converted in a digital-to-analogue converter into an analogue control signal and fed to a driver circuit consisting a pre-amplifier and an output amplifier. This driver circuit outputs a current, corresponding to the correction value, to a correction coil. The magnitude of the correction current also depends on the gain of the driver circuit, and can therefore vary from receiver to receiver. This is the reason why it has therefore been known in the prior art to design the basic amplification of the driver circuits such that the required deflection is ensured for the maximum correction value even in the case of the smallest value to be expected for the gain. However, this means at the same time that the full range of the correction values cannot be utilized at all in the case of a driver circuit with a large gain. The result of this is an unnecessary limitation of the resolution of the convergence correction.